Successive appromixation analog/digital converter and associated integrated component and conversion method

ABSTRACT

A successive approximation analog/digital converter is provided, which includes a successive approximation register supplying a digital/analog converter, first means of comparing an input signal of the analog/digital converter to an output signal of the digital/analog converter delivering a first comparison signal, said successive approximation analog/digital converter being synchronised by a clock signal coming from a conversion clock. A method such as this includes dynamic adaptation of the conversion clock period based on at least one parameter.

CROSS-REFERENCE TO RELATED APPLICATION

None.

FIELD OF THE DISCLOSURE

The field of the disclosure is that of analog/digital converters, andmore particularly successive-approximation type analog/digitalconverters.

More precisely, the disclosure relates to generating the clock for asuccessive-approximation type analog/digital converter (hereinafterdesignated as successive approximation ADC).

BACKGROUND OF THE DISCLOSURE

A simplified block diagram of a conventional successive approximationanalog/digital converter 1000 is shown in FIG. 1.

The successive approximation ADC 1000 includes:

-   -   an digital/analog converter 110 (hereinafter referenced as DAC);    -   a sample-and-hold device 150, the input of which corresponds to        the successive approximation ADC 1000 input, and which is        therefore supplied with the ADC 1000 input voltage, hereinafter        referenced as voltage VIN, and the output of which, supplying a        voltage hereinafter referenced as voltage Vin1, is connected to        the input of a comparator 120 described hereinbelow. The voltage        Vin1 is equal to the input voltage Vin at the end of the        sampling phase (described hereinbelow). The sample-and-hold        device 150 enables the input voltage Vin of the successive        approximation ADC 1000 to be stabilised during the conversion        phase;    -   a comparator 120 of which a first input 121 is supplied with the        output voltage Vin1 of the sample-and-hold device 150, a second        input 122 is supplied with an output voltage (analog) of the DAC        110 (hereinafter referenced as Vdac) delivered to an output 112        of the DAC 110 and an output 123 delivering an output voltage        hereinafter referenced as Vcomp;    -   a successive approximation register 130 (SAR) of which a first        input 131 is supplied with the output voltage Vcomp, a second        input 132 is supplied with a voltage delivered by a conversion        clock hereinafter referenced as CLK, and a set of n outputs        (hereinafter referenced as a1, a2, . . . , an) 133 (n being a        natural number equal to 10, for example) which supplies n inputs        111 of the DAC 110;    -   a circuit (optional) for storing the conversion result 140 of        which a first input 141 is supplied by the output voltage Vcomp,        n second inputs 142 are connected to the n outputs 133,        respectively, of the register 130 and n outputs (hereinafter        referenced as b1 to bn) 143 deliver the successive approximation        ADC output voltage hereinafter referenced as Vout.

A complete conversion cycle includes a sampling phase and a conversionphase. A cycle such as this requires m period(s) of the conversion clock(m being a natural number greater than or equal to one) for the samplingoperation and n period(s) of the conversion clock for the analog-digitalconversion operation (n being the number of bits). For example, it willhereinafter be assumed that the conversion operation is carried out onn=10 bits and that the sampling operation is carried out on 3 bits.

The conversion clock period of a conventional successive approximationADC 1000 such as this is initially set as constant and remains sothroughout the entire conversion cycle.

The choice of the conversion clock period depends on the DAC 110 set-uptime and on the comparator 120 response time.

FIG. 2 shows time-dependent curves for the CLK voltages and the signals,referenced as d<9:0>, coming from the outputs b1 to bn, over oneconversion phase (step 0 to step 9).

During a conversion phase 201, the output 112 of the DAC 110 generatesan output voltage Vdac which, in a first conversion step, assumes afirst value Vref/2 (which corresponds to a “1” on the bit of the outputa1 of the SAR 130). In a second conversion step, based on the voltage atthe output 123 of the comparator 120, the output a1 is maintained at “1”or reset to “0,” and the output Vdac assumes the value a1*Vref/2+Vref/4(which corresponds to a “1) on the bit of the output a2 of the SAR 130).In a tenth conversion step, based on the voltage at the output 123 ofthe comparator 120, the output a9 is maintained at “1” or reset to “0,”the voltage Vdac assumes a valuea1*Vref/2+a2*Vref/4+a3*Vref/8+a4*Vref/16+a5*Vref/32+a6*Vref/64+a7*Vref/128+a8*Vref/256+a9*Vref/512+Vref/1024(which corresponds to a “1” on the bit of the output a10 of the SAR130), Vref being a constant reference voltage. Finally, based on thevoltage at the output 123 of the comparator 120, the output a10 ismaintained at “1” or reset to “0”.

Hereinafter, the bit of the output al will be designated as the mostsignificant bit (hereinafter designated as MSB), and the bit of theoutput a10 as the least significant bit (hereinafter designated as LSB).

Over the course of a conversion phase, the comparator 120 compares theoutput voltage Vdac to the input voltage Vin, for each of the aforesaidsteps. The results of these comparisons, hereinafter referenced as b1,b2, . . . and b10, are stored in the conversion result storage circuit140.

The clock frequency is limited both by the DAC 110 converter set-up timeand by the comparator 120 response time.

For each conversion step of the conversion phase, Vdac must beestablished with a degree of accuracy at least equal to half the valueof the least significant bit (LSB) which assumes the value Vref/1024.

FIG. 3 shows the evolution of the signal Vdac in relation to time t, inthe case where Vdac assumes the value of the least significant bit(curve 301) and in the case where Vdac assumes the value of the mostsignificant bit (curve 302).

Thus, Vdac assumes a time t1 in order to be established with a degree ofaccuracy at least equal to half the value of the least significant bit(LSB), and a time t2 in order to be established with a degree ofaccuracy at least equal to the least significant bit (LMSB). It can benoted that t1 is much less than t2.

The output voltage Vcomp of the comparator 120 can switch from 0 to 1 orfrom 1 to 0. The response time of the comparator 120 depends on theabsolute value of the difference between the input voltage Vin of thesuccessive approximation ADC 1000 and the output voltage Vdac of the DAC110.

FIGS. 4 and 5, respectively, show curves of the voltages Vin, Vdac,Vcomp and CLK (in V), in relation to time (in s), in the case where thevoltage Vdac is substantially equal to 0.0207 V and Vin is substantiallyequal to 0.380 V (FIG. 4), and in a case where the voltage Vdac issubstantially equal to 0.380 V and Vin is substantially equal to 0.383 V(FIG. 5).

Thus, in the case where the voltage Vdac is substantially equal to 0.207V and Vin is substantially equal to 0.380 V, the comparator 120 responsetime equals 16 ns, and in the case where the voltage Vdac issubstantially equal to 0.380 V and Vin is substantially equal to 0.383V, the comparator 120 response time equal 47 ns.

Consequently, the lower the absolute value of the difference between Vinand Vdac, the longer the comparator 120 response time.

A new value for the output voltage of the DAC 110 (corresponding to anew conversion step) is applied to the second input 122 of thecomparator 120 so as to be synchronised with a current rise or fall inthe clock CLK voltage, and then the value of the output voltage of thecomparator 120, corresponding to the comparison of this new value forthe output voltage of the ADC 110 with Vin1, is stored during thefollowing rise or fall in the clock CLK voltage.

Thus, the minimum conversion clock period corresponds to the sum of theDAC 110 converter set-up time and the comparator 120 response time.

In a conventional successive approximation ADC, in order to ensure thatthe conversion clock period will be sufficiently long to be able tocarry out the conversion operation with the degree of accuracy requiredfor all of the values of the signal Vin, a clock period is generallychosen which is constant and equal to the sum of the DAC converterset-up time, in the case of the most significant bit (MSB) and thecomparator response time, in the case of the slightest differencebetween the voltage Vin and the voltage Vdac (substantially equal to thevalue of the least significant bit or LSB).

In this way, one is placed in the least favourable situation in terms ofthe speed of the conversion operation, and, at each of the conversionsteps, a loss of conversion time is thus observed for the majority ofthe input voltages Vin.

This loss of time is shown in relation to FIG. 6, which shows voltagecurves Vin, Vdac, Vcomp and CLK (in V) in relation to time t (in μs), ina case where Vin is substantially equal to 0.7 V and where theconversion clock period is substantially equal to 0.2 μs.

A switching of the comparator 120 is observed at the moment when Vdacassumes a value of approximately 0.4 V. It can be observed that, inorder for Vdac to be equal to 0.4 V, the sum of the DAC 110 converterset-up time and the comparator response time (which is of the order of0.02 μs) is much lower than the conversion clock period. Thus, in thecase of this conversion step, a time loss of substantially 0.18 μs isobserved.

SUMMARY

An aspect of the disclosure relates to a successive approximationanalog/digital converter comprising a successive approximation registersupplying a digital/analog converter, first means of comparing an inputsignal of the analog/digital converter to an output signal of thedigital/analog converter delivering a first comparison signal, saidsuccessive approximation analog/digital converter being synchronised bya clock signal coming from a conversion clock.

The converter includes means for dynamic adaptation of the conversionclock period on the basis of at least one parameter and the means fordynamic adaptation of the conversion clock period include means ofmeasuring at least one response time of the first means of comparisonand/or means of measuring at least one set-up time for at least oneanalog voltage via the digital/analog converter.

The basic principle of an aspect of the disclosure is based on thedynamic adaptation of the conversion clock period of a successiveapproximation ADC, whereby the period is reduced when it is notdetrimental to the quality of the conversion operation.

Thus, this dynamic adaptation of the conversion clock period enablesimprovement in the conversion speed of a successive approximationanalog/digital converter.

In comparison with the case of a clock the period of which is constant,this adaptation makes it possible, in particular, to reduce the amountof time lost during the conversion phase, which is due to the conversionclock period.

The means for dynamic adaptation of the conversion clock periodpreferably include means of measuring at least one response time of thefirst means of comparison and/or means of measuring at least oneset-time for at least one analog voltage via the digital-analogconverter.

Thus, for example, the parameter is at least one response time of thefirst means of comparison and/or at least one time for setting up atleast one analog voltage via the digital/analog converter.

According to one advantageous characteristic of the disclosure, themeasurement means include second means of comparing the input signal ofthe analog/digital converter to the output signal of the digital/analogconverter delivering a second comparison signal supplying means ofgenerating said conversion clock, and the means of generating saidconversion clock take account of the first and second comparisonsignals.

The measurement means are advantageously adapted for also measuring atleast one response time of the second means of comparison.

Preferably, the first means of comparison include a first comparator,the second means of comparison include a second comparator, and thefirst and second comparators are identical.

According to one embodiment of the disclosure, the second means ofcomparison include means of multiplexing the input signal of theanalog/digital converter and the output signal of the digital/analogconverter to first and second inputs of the second comparator takingaccount of the clock signal.

The multiplexing means advantageously include at least one interruptercontrolled by the clock signal and at least one interrupter controlledby the inverse of the clock signal.

Said means of generating the conversion clock advantageously include atleast one EXCLUSIVE-OR gate.

Said means of generating the conversion clock preferably includetime-delay means applied to said clock signal.

Thus, a time delay makes it possible to guarantee a minimum clock periodwidth, in particular for the logic implemented in the successiveapproximation register.

According to one embodiment of the disclosure, the means of generatingthe conversion clock include means of reducing the clock signal period.

It is thus possible to obtain a clock signal the clock period of whichis optimised throughout the conversion phase.

Said means of reducing the clock period advantageously include twoinverters mounted in serial.

Said means of reducing the clock period advantageously include means ofinsulating the analog/digital converter from noise generated by thedynamic adaptation means.

Said insulation means preferably include at least one follower amplifierassembly.

According to one embodiment of the disclosure, said at least oneparameter belongs to the group comprising the:

-   -   response time of the first comparison means;    -   time for setting up at least one analog voltage via the        digital-analog converter;    -   input signal of the analog/digital converter;    -   operating temperature of the analog/digital converter;    -   method of manufacturing the analog/digital converter.

The disclosure also relates to an integrated component comprising atleast one successive approximation analog/digital converter as describedpreviously.

The disclosure also relates to a successive approximation method ofconverting an analog input signal into a digital output signal, which isimplemented by a successive approximation analog/digital convertercomprising a successive approximation register supplying adigital/analog converter, first means of comparing an input signal ofthe analog/digital converter to an output signal of the digital/analogconverter delivering a first comparison signal.

Said successive approximation conversion is synchronised by a clocksignal coming from a conversion clock.

The method includes a step for dynamic adaptation of the conversionclock period based on at least one parameter and the step for dynamicadaptation of the conversion clock period includes a step for measuringat least one response time of the first comparison means and/or a stepfor measuring at least one set-up time for at least one analog voltagevia the digital/analog converter.

The advantages of the integrated component and of the successiveapproximation conversion operation are substantially the same as thoseof the successive approximation method, and are not specified morefully.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages will become more apparent uponreading the following description of particular embodiments, given aspurely illustrative and non-limiting examples, and of the appendeddrawings, in which:

FIG. 1 is a simplified block diagram of a conventional successiveapproximation analog/digital converter;

FIG. 2 shows time-dependent curves of the voltages CLK and signalscoming from the outputs b1 to bn, over one conversion phase of theconventional successive approximation ADC of FIG. 1;

FIG. 3 shows curves of the signal Vdac in relation to time t, in thecase where Vdac assumes the value of the least significant bit (curve301), and in the case where Vdac assumes the value of the mostsignificant bit (curve 302);

FIGS. 4 and 5 show curves for the voltages Vin, Vdac, Vcomp and CLK (inV) in relation to time t (in s), in the case where the voltage Vdac issubstantially equal to 0.207 V and Vin is substantially equal to 0.380 V(FIG. 4), and in the case where the voltage Vdac is substantially equalto 0.380 V and Vin is substantially equal to 0.383 V;

FIG. 6 shows curves for voltages Vin, Vdac, Vcomp and CLK (in V), inrelation to time t (in ηs), in the case where Vin is substantially equalto 0.7 V and where the conversion clock period is substantially equal to0.2 μs;

FIG. 7 shows a simplified block diagram of a successive approximationanalog/digital converter according to one particular embodiment of thedisclosure;

FIG. 8, according to one particular embodiment of the disclosure, showsa detailed circuit diagram of the dynamic adaptation circuit for theconversion clock period of the successive approximation ADC of FIG. 7;

FIG. 9 shows curves showing the evolution, in relation to time t, of thevoltages Vstart, Veoc, Vdac, Vin, Vcomp33, Vnet145, VCLKREF, Vincomp1and Vincomp2 at the beginning of a conversion phase of the successiveapproximation ADC of FIG. 7;

FIG. 10 shows a diagram of a particular implementation of the successiveapproximation analog/digital converter of FIG. 7; and

FIGS. 11A to 11D are diagrams representing the conversion error and timefrequency distribution in the case where, in accordance with anexemplary aspect of the disclosure, dynamic adaptation of the conversionclock period is implemented (FIGS. 11C and 11D), and in the conventionalcase where the conversion clock period is constant (FIGS. 11A and 11B).

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 7 shows a simplified block diagram of a successive approximationanalog/digital converter according to one particular embodiment of thedisclosure.

The successive approximation ADC 7000 includes:

-   -   a digital/analog converter 710 (hereinafter referenced as DAC)        supplied at a first input 712 with a constant reference voltage        (or signal) Vref;    -   a sample-and-hold device 750 of which a first input 751 is        supplied with the input voltage (or signal) Vin (analog) of the        successive approximation ADC, a second input 753 is connected to        a first output 735 of the SAR 730 which delivers a hold signal,        hereinafter referenced as Vhold, and an output 754 delivers a        signal Vin1 the value of which is stable and the value of which        is equal to that of the input voltage Vin at the end of the        sampling period, during the conversion phase;    -   a first comparator 720 of which a first input 721 is supplied        with the voltage (or signal) Vin1 delivered to the output 754 of        the sample-and-hold device 750, a second input 722 is supplied        with an output voltage (or signal) (analog) of the DAC 710        (hereinafter referenced as Vdac) delivered to an output 713 of        the DAC 710, and an output 723 delivers an output voltage (or        signal) (or first comparison voltage resulting from the        comparison of the voltages Vin1 and Vdac) hereinafter referenced        as Vcomp33;    -   a successive approximation register 730 (SAR) of which a first        input 731 is supplied with the output voltage Vcomp33, a second        input 732 is supplied with a clock voltage (or signal)        (hereinafter referenced as VCLKREF) delivered by a circuit 760        for dynamic adaptation of the conversion clock period described        hereinbelow, a third input 733 is supplied with an        initialisation signal hereinafter referenced as “Vstart,” an        output 734 delivering an end-of-conversion-cycle indication        signal (or EOC for “End of Cycle”) hereinafter referenced as        Veoc, and a set of n second outputs (hereinafter referenced by        a1 to a10) 736 which supply n second inputs 711 of the DAC 719        (n is the number of bits of the conversion operation, and        hereinafter, for example, it is chosen to be equal to 10);    -   a circuit for dynamic adaptation 760 of the conversion clock        period of the successive approximation ADC 7000.

It can be noted that, in the same way as the successive approximationADC 1000 of FIG. 1, the successive approximation ADC 7000 can(optionally) include a storage circuit (not shown in FIGS. 7, 8 and 10)serving to store the end-of-conversion results. This storage circuit isnot indispensable to the operation of the successive approximation ADCaccording to the disclosure.

In this particular embodiment of the disclosure, this circuit 760includes a multiplexer 761, a second comparator 762, which is identicalto the first comparator 720, and a clock generator 763.

The multiplexer 761 includes:

-   -   a first input 7611 connected to the output 754 (delivering the        voltage Vin1) of the sample-and-hold device 750;    -   a second input 7612 connected to the output 713 of the DAC 710        delivering the voltage Vdac;    -   a third input 7613 connected to the output 7633 (delivering the        clock voltage VCLKREF) of the clock generator 763;    -   a first output 7614 connected to a first input 7621 of the        second comparator 762; and    -   a second output 7615 connected to a second input 7622 of the        second comparator 762.

The multiplexer 761 functions as a switch connecting the signals Vin1and Vdac to the first 7621 and second 7622 inputs, respectively, of thesecond comparator 762, during the half clock period CLKREF and to thesecond 7622 and first 7621 inputs, respectively, of the secondcomparator 762 during the half clock period CLKREF.

The second comparator 762 includes an output 7623 delivering an outputvoltage (or second comparison voltage) hereinafter referenced as Vnet145(resulting from the comparison of the voltages applied to its first 7621and second 7622 inputs by the first 7614 and second 7615 outputs of themultiplexer 761) and connected to a first input 7631 of the clockgenerator 763.

The clock generator 763 includes a first input 7631 connected to theoutput 7623 of the second comparator 762, a second input 7632 connectedto the output 723 delivering the voltage Vcomp33 of the first comparator720 and an output 7633 which delivers the clock voltage VCLKREF andwhich is connected to the second input 732 of the successiveapproximation register 730 and to the third input 7613 of themultiplexer 761.

FIG. 8 shows a detailed block diagram of the circuit for dynamicadaptation 760 (shown in FIG. 7) of the conversion clock periodaccording to one particular embodiment of the disclosure.

Thus, the multiplexer 761 is produced by means of:

-   -   first 7616 and second 7617 interrupters connecting the first        7611 input of the multiplexer 761 (which receives the voltage        Vdac) to the first 7614 output of the multiplexer 761 (which        delivers a voltage referenced hereinafter as Vincomp1) and the        second 7612 input of the multiplexer 761 (which receives the        voltage Vin1) to the first 7614 output of the multiplexer 761        (which delivers a voltage referenced hereinafter as Vincomp2),        respectively, and which are controlled by the voltage VCLKREF        and by the inverse of the voltage VCLKREF, respectively.    -   third 7618 and fourth 7619 interrupters connecting the second        7612 input of the multiplexer 761 (which receives the voltage        Vin1) to the second 7615 output of the multiplexer 761 (which        delivers a voltage referenced hereinafter as Vincomp2) and the        first 7611 input of the multiplexer 761 (which receives the        voltage Vdac) to the second 7615 output of the multiplexer 761        (which delivers a voltage referenced hereinafter as Vincomp1),        respectively, and which are controlled by the voltage VCLKREF        and by the inverse of the voltage VCLKREF, respectively.

The clock generator 763 is produced by means of an EXCLUSIVE-OR gate thefirst and second inputs of which are connected to the first 7631 andsecond 7632 inputs of the clock generator 763, and the output of which,delivering an output voltage referenced hereinafter as VCOMPREF, isconnected to a time-delay device 7635 (which is also part of the clockgenerator 763) the output of which is connected to the output 763 of theclock generator 763 (which delivers the voltage VCLKREF).

It is to be noted that the clock generator 763 may not include anytime-delay device.

During a conversion phase, the output 713 of the DAC 710 generatesdecreasing voltages Vdac, according to the known and previouslydescribed principle of successive approximation converters. In a firstconversion step, Vdac assumes a first value Vref/2 (which corresponds toa 1 at the second output a1 of the SAR 730).

The bits delivered by the second outputs a1 and a10 of the SAR 730 arethe most significant bit (MSB) and the least significant bit (LSB),respectively.

The successive approximation register 730 sequences the analog/digitalconversion (as described in detail below in relation to FIG. 9) byimposing a value of 1 to the most significant bit (MSB) of the secondoutput a1 of the SAR 730, and then it controls the output 723 of thefirst comparator 720 so as to verify if the voltage Vdac is greater orless than the voltage Vin1. The voltage Vin1 is equal to the voltage Vinat the end of the sampling phase.

If the voltage Vdac is greater than Vin, then the successiveapproximation register 730 imposes a 0 on the bit of the second outputa1 (MSB) of the SAR 730 and it imposes a value of 1 on the bit of thesecond output a2 of the SAR 730, and next, control of the output of thefirst comparator 720 is repeated.

In the opposite case, if the voltage Vin is greater than the voltageVdac, then the successive approximation register 730 maintains a 1 onthe bit of the second output a1 (MSB) of the SAR 730, and it imposes avalue of 1 on the bit of the second output a2 of the SAR 730, and thencontrol of the output of the first comparator 720 is repeated.

Thus, the time required for the 10-bit conversion phase of an analogvoltage into a digital voltage is n=10 conversion clock periods (n isthe number of bits of the analog/digital converter). To this time isadded the length (m clock periods) of the sampling phase, during whichthe output Vin is connected to the output Vin1. The total conversiontime is (m+n) clock periods.

The sample-and-hold device 750 is used to sample the input voltage Vinof the successive approximation ADC 7000 during the sampling phase andto keep it stable during the conversion phase.

The circuit 760 for dynamic adaptation of the conversion clock period isused to generate a clock voltage VCLKREF the period and cyclic ratio ofwhich are dynamically adapted for each of the n=10 clock periods, inparticular, based on;

-   -   the DAC 710 converter set-up time (dependent on the Vdac voltage        to be set up) and    -   the response time of the first comparator 720, of that of the        second comparator 762 and of the multiplexer 761 (depending, in        particular, on the difference in voltage between Vin And Vdac).

According to alternative embodiments of this disclosure, the conversionclock period is dynamically adapted, in particular on the basis of atleast one of the following parameters:

-   -   the DAC 710 converter set-up time (dependent on the Vdac voltage        to be set up) and    -   the response time of the first comparator 720, of that of the        second comparator 762 and of the multiplexer 761 (dependent, in        particular, on the difference in voltage between Vin and Vdac);    -   the input signal Vin of the analog/digital converter;    -   the operating temperature of the ADC 7000;    -   the ADC 7000 manufacturing method.

This adaptation is carried out by measuring the set-up time of theoutput voltage of the first comparator 720 and second comparator 762.This measurement takes account of the ADC 710 set-up time. The clocktransitions take place either at the first 723 or the second 763 outputof the comparators 720 and 762.

As illustrated hereinbelow, in relation to FIG. 9, the adaptationcircuit 760 ensures the generation of two transitions for eachconversion clock VCLKREF period regardless of the Vref voltage and Vinvoltage to be converted.

As a matter of fact, the voltage Vcomp33, which depends on the absolutevalue of the difference between the voltages Vin and Vdac, does notswitch from 0 to 1 at each conversion step. Thus, the multiplexer 761and the first comparator 762 of the adaptation circuit 760 areresponsible for generating the missing clock transitions which cannot beextracted from the voltage Vcomp33.

The voltages Vincomp1 and Vincomp2 are equal to Vdac and Vin,respectively, during a first portion of a clock period, and are equal toVin and Vdac, respectively, during a second portion of the clock period.This mechanism of switching to Vincomp1 and Vincomp2 enables measurementof the response time of the first comparator 720 at the output 7623 ofthe second comparator 762, at the end of each first clock periodportion, and makes it possible to provide additional clock transitions(not present at the output 723 of the comparator 720) to the clockvoltage VCLKREF for each end of the second clock period VCLKREF. Thetime-delay device 7635 makes it possible to guarantee a minimum clockperiod width for the SAR 730 logic.

FIG. 9 shows the operating principle of the circuit 760 for dynamicadaptation of the conversion clock period according to one particularembodiment of the disclosure shown in FIGS. 7 and 8.

FIG. 9 shows an example of the evolution of the voltages Vstart, Veoc,Vdac, Vin, Vcomp33, Vnet145, VCLKREF, Vincomp1 and Vincomp2, in relationto time t, at the beginning of a conversion phase.

Hereinafter, when speaking of high and low voltage values, for example,it is understood to mean a logic value of 1 and a logic value of 0,respectively.

Prior to the start of the conversion phase, for example, a samplingphase is carried out over three conversion clock periods.

The voltage Vref is a pre-selected constant reference voltage. It isequal to the maximum input voltage Vin anticipated at the input of thesuccessive approximation ADC 7000.

The voltage Vref is associated with the technology used. For example, itis between 1 V and 1.8 V for 0.18-μm technology.

The given input voltage Vin of the ADC 7000 is stored in thesample-and-hold device 750 during the sampling phase.

At the end of the sampling phase, the voltage Vin applied to the firstinput 721 of the first comparator 720 and to the first input 7611 of themultiplexer 761 is equal to Vin1.

In a sub-step 1, a pulse signal Vstart is applied to the third input 733of the successive approximation register 730. Then, the voltage Veocshifts from a high value to a low value (e.g., 0V). In the same way, thevoltage VCLKREF shifts from a high value to a low value.

Then, in a sub-step 2, the ADC 7000 switches from the sampling phase tothe conversion phase. The voltage at the sample-and-hold device output750 remains set at Vin1 during the conversion phase, when the secondinput 753 is clamped at 1 by the SAR 730. The sample-and-hold device 750then shifts to the “input voltage hold” mode.

For example, a Vin value of between Vref/4 and Vref/4+Vref/8 is chosen.

Due to the fact that the signal Veoc is at its low value, the voltageVCLKREF is a copy of the voltage VCOMPREF offset by the time delay 7635(as indicated above, a time delay 7635 such as this is implemented so asto ensure a minimum value for the conversion clock period). For example,the time delay is 20 ns.

The DAC 710 therefore applies a voltage Vref/2, corresponding to theMSB, to the second input 722 of the first comparator 720, and to theinput 7612 of the multiplexer 761.

Due to the fact that the voltage Vin1 applied to the first input 721 ofthe first comparator 720 and the input 7611 of the multiplexer 761 islower than the voltage Vdac=Vref/2 applied to the second input 722 ofthe first comparator 720 and to the input 7612 of the multiplexer 761,the voltage Vcomp33 (delivered by the output 723 of the first comparator720) is at its low value.

In a sub-step 3, due to the fact that the voltage VCLKREF is at its lowvalue, the voltage Vincomp1 is equal to the voltage Vdac (which is alsoapplied to the second input 722 of the first comparator 720) and thevoltage Vincomp2 is equal to the voltage Vin1 (which is also applied tothe first input 721 of the first comparator 720), the voltage Vnet145thus assumes its high value, after the response time of the secondcomparator 762 has elapsed (which depends on the difference between thevoltage Vincomp1=Vdac and the voltage Vincomp2 Vin1).

Thus, the voltage VCOMPREF, which is the output of the EXCLUSIVE-OR gate7634 (to which Vcomp33 and Vnet145 is applied), assumes its high value.Thus, VCLKREF assumes its high value in a sub-step 4 (following theoffset due to the time delay 7635).

In a sub-step 5, due to the fact that the voltage VCLKREF is at its highvalue, the voltage Vincomp1 is equal to the voltage Vin1 (which is alsoapplied to the first input 721 of the first comparator 720) and thevoltage Vincomp2 is equal to the voltage Vdac (which is also applied tothe second input 722 of the first comparator 720), the voltage Vnet145thus assumes its low value, after the response time of the secondcomparator 762 has elapsed (which depends on the difference between thevoltage Vincomp1=Vin1 and the voltage Vincomp2=Vdac). Thus, the inputsof the second comparator 762 are inverted after VCLKREF has beenswitched.

Therefore, the voltage VCOMPREF, which is the output of the EXCLUSIVE-ORgate 7634 (to which the Vcomp33 and Vnet145 are applied), assumes itslow value. Thus, VCLKREF assumes its low value in sub-step 6 (followingthe offset due to the time delay 7635).

Then, the low value of the voltage Vcomp33 results in a resetting of themost significant bit (MSB) to 0 at the second output al of thesuccessive approximation register 730, at the moment when VCLKREFassumes its low value.

In a sub-step 7, the DAC 710 applies a voltage Vref/4 to the secondinput 722 of the first comparator 720 and to the input 7612 of themultiplexer 761 (after the time for setting up this voltage Vref/4 bythe DAC 710 has elapsed).

In a sub-step 8, due to the fact that the voltage Vin1 applied to thefirst input 721 of the first comparator 720 is higher than the voltageVdac=Vref/4 applied to the second input 722 of the first comparator 720,the voltage Vcomp33 assumes its high value, after the response time ofthe first comparator 720 has elapsed (which depends on the differencebetween the voltage Vin1 and the voltage Vdac=Vref/4).

Due to the fact that the voltage VCLKREF is at its low value, thevoltage Vincomp1 is equal to the voltage Vdac and the voltage Vincomp2is equal to the voltage Vin1 (which is higher than the voltage Vdac),thus, the voltage Vnet145 retains its low value.

Therefore, the voltage VCOMPREF assumes its high value. In this way, ina sub-step 9, VCLKREF assumes its high value (following the offset dueto the time delay 7635).

In a sub-step 10, due to the fact that the voltage VCLKREF is at its lowvalue, the voltage Vincomp1 becomes equal to the voltage Vin1, and thevoltage Vincomp2 becomes equal to the voltage Vdac (which is lower thanVin), and thus, after the response time of the second comparator 762 haselapsed (which depends on the difference between the voltageVincomp1=Vin1 and the voltage Vincomp2=Vdac), the voltage Vnet145assumes its high value.

Thus, in a sub-step 11, VCOMPREF, which is the output of theEXCLUSIVE-OR gate 7634 (to which Vcomp33 and Vnet145 are applied),assumes its low value, and VCLKREF assumes its low value (following theoffset due to the time delay 7635). Thus, the inputs of the secondcomparator 762 are inverted after VCLKREF has been switched.

Then, due to the fact that the voltage Vin1 is higher than the voltageVdac, the value of 1 is maintained at the second output a2 of thesuccessive approximation register 730, at the moment when VCLKREFassumes its low value.

Thus, in a sub-step 12, the DAC 710 applies a voltage Vref/4+Vref/8(after the time for setting up this voltage Vref/4+Vref/8 by the DAC 710has elapsed) to the second input 722 of the first comparator 720 and tothe input 7612 of the multiplexer 761.

In a sub-step 13, due to the fact that the voltage Vin1 applied to thefirst input 721 of the first comparator 720 is lower than the voltageVdac=Vref/4+Vref/8 applied to the second input 722 of the firstcomparator 720, the voltage Vcomp33 assumes its low value after theresponse time of the first comparator 720 has elapsed (which depends onthe difference between the voltage Vin1 and the voltageVdac=Vref/4+Vref/8).

Due to the fact that the voltage VCLKREF is at its low value, thevoltage Vincomp1 is equal to the voltage Vin1 and the voltage Vincomp2is equal to the voltage Vdac (which is lower than the voltage Vin1), thevoltage Vnet145 thus retains its high value.

Thus, the voltage VCOMPREF assumes its high value. In this way, in asub-step 14, VCLKREF assumes its high value (following the offset due tothe time delay 7635).

The method is repeated in this way until the end of the conversion phase(for the sake of clarity, only sub-steps 1 to 14 have been shown in thisFIG. 9). As a matter of fact, at the end of the tenth conversion clockperiod (thus at the end of the tenth conversion step), the voltage Veocre-assumes its high value and the voltage VCLKREF is replaced with avoltage VCLK delivered by an external clock by means of aninverter-based 773 circuit 770 (shown below in FIG. 10) with two ANDgates 771 and one OR gate 772.

In this way, the complementary switching operations of the first 762 andsecond 763 multiplexers are used in combination with the switchingoperations of the output of the first comparator 720 in order togenerate the leading and trailing edges of the conversion clock VCLKREF.Owing to the present disclosure, therefore, the period and cyclic ratioof this clock VCLKREF are adapted continuously during the conversionphase, on the basis of the DAC 710 set-up times and response times ofthe first comparator 720, on the one hand, and of the multiplexer 761and second comparator 762, on the other hand.

The comparators 720 and 762 are preferably identical, in order to obtainvery close propagation times for a given difference in voltage|Vin1−Vdac|.

According to a preferred embodiment of the disclosure, the multiplexer761 switching time is chosen to be as short as possible, and is muchless than the comparator response time.

FIG. 10 shows a diagram of one particular implementation of thesuccessive approximation analog/digital converter 7000, according to theparticular embodiment of the disclosure.

For the sake of clarity, only one link is shown between the ten outputs736 of the SAR 730 and ten inputs 711 of the DAC 710.

In FIG. 10:

-   -   no time delay 7635 has been shown;    -   the inverted voltage VCLKREF is designated by VCOMPREFB;    -   two follower amplifier-type assemblies 781 and 782 are        implemented between the first output 754 of the sample-and-hold        device 750 and the first input 7611 of the multiplexer 761, and        between the second output 755 of the sample-and-hold device 750        and the second input 7612 of the multiplexer 761, respectively,        so as to insulate the dynamic adaptation circuit 760 from the        sample-and-hold device 750, in order to prevent the noise        resulting from the switching of the interrupters 7616 to 7619        from interfering with the sample-and-hold device 750.

In this implementation, two inverters 791 and 792 acting as buffers areused at the output of the EXCLUSIVE-OR gate 7634, so as to reduce therise and fall times of the voltage VCOMPREF.

FIGS. 11A to 11D are diagrams showing error distribution (or integralnon-linearity or INL) in LSB in the encoding of Vin and the conversiontime distribution (in s) of the successive approximation ADC 7000, inthe case where dynamic adaptation of the conversion clock period isimplemented (FIGS. 11C and 11D), and in the conventional case where theconversion clock period is constant (FIGS. 11A and 11B).

In the graphs of FIGS. 11A and 11C, the x-axis represents error orintegral non-linearity in LSB, and the y-axis represents the number ofvoltage values Vin (between 0 and 1024) which have been encoded with agiven error.

In the graphs of FIGS. 11B and 11D, the x-axis represents error orintegral non-linearity in LSB, and the y-axis represents the number ofvoltage values Vin (between 0 and 1024) which have been encoded with agiven conversion time.

It can be noted that, by implementing the dynamic adaptation of theconversion clock period in accordance with the disclosure, it ispossible to:

-   -   shorten the duration of the conversion phase. The total duration        of the conversion phase varying from 1.4 μS to 1.6 μS, based on        the input voltage; the total duration of the conversion phase        otherwise being 2.6 μS with the conventional solution wherein        the conversion clock period is constant;    -   keep the conversion errors lower than or equal to those obtained        with the conventional solution wherein the conversion clock        period is constant. Integral non-linearity is the difference        between the digital code obtained, on the one hand, at the        output of an ideal ADC and, on the other hand, at the output of        the converter tested, with either a variable-pitch clock, in        accordance with the disclosure, or with the conventional        solution wherein the conversion clock period is constant.

Of course, a circuit for dynamic adaptation of the conversion clockperiod according to the disclosure can be implemented in any successiveapproximation analog/digital converter.

In addition, this disclosure applies, in particular, to both successiveapproximation ADC architectures using switched capacitors and tosuccessive approximation ADC architectures using linear techniques.

It is recalled that linear techniques use resistive or currentgenerator-based components, as well as amplifiers.

Non-linear techniques use capacitors switched by a reference clock, soas to emulate resistive components and current sources. The advantage ofswitched capacitors is based on the accuracy of clock-dependent devices(which can be very accurate) and on the matching of (well-controlled)capacitive components.

One or more aspects of the present disclosure mitigate inconveniences ofthe prior.

More precisely, at least one of the embodiments of the disclosureprovides a technique enabling improvement in the conversion speed of asuccessive approximation analog/digital converter.

At least one of embodiment of the disclosure implements such a techniquewhich, in particular, makes it possible to reduce the time lost duringthe conversion phase, which is due to the conversion clock period.

At least one of embodiment of the disclosure provides such a techniquesuch as this which can be implemented simply and inexpensively.

Although the present disclosure has been described with reference to oneor more examples, workers skilled in the art will recognize that changesmay be made in form and detail without departing from the spirit andscope of the disclosure or the appended claims.

1. Successive approximation analog/digital converter comprising: a successive approximation register supplying a digital/analog converter, and being synchronised by a clock signal coming from a conversion clock; a first comparator comparing an input signal of the analog/digital converter to an output signal of the digital/analog converter and delivering a first comparison signal; and a dynamic adaptation circuit, which dynamically adapts the conversion clock period based on at least one parameter, wherein the dynamic adaptation circuit includes a measurement circuit, which measures at least one of: (a) at least one response time of the first comparator; or (b) at least one set-up time for at least one analog voltage via the digital/analog converter.
 2. Converter of claim 1, wherein the measurement circuit includes a second comparator comparing the input signal of the analog/digital converter to the output signal of the digital/analog converter and delivering a second comparison signal supplying a clock generator, which generates said conversion clock, wherein the clock generator takes account of said first and second comparison signals.
 3. Converter of claim 2, wherein the measurement circuit is adapted for also measuring at least one response time of the second comparison means.
 4. Converter of claim 2, wherein the first and second comparators are identical.
 5. Converter of claim 4, wherein the measurement circuit includes a multiplexer, which multiplexes the input signal of the analog/digital converter and the output signal of the digital/analog converter to the first and second inputs of the second comparator taking account of the clock signal.
 6. Converter of claim 5, wherein the multiplexer includes at least one interrupter controlled by the clock signal and at least one interrupter controlled by the inverse of the clock signal.
 7. Converter of claim 2, wherein said clock generator includes at least one EXCLUSIVE-OR gate.
 8. Converter of claim 2, wherein said clock generator includes a time-delay device applied to said clock signal.
 9. Converter claim 1, wherein the dynamic adaptation circuit includes an insulator, which insulates the analog/digital converter from noise generated by the dynamic adaptation circuit.
 10. Converter of claim 9, wherein said insulator includes at least one follower amplifier assembly.
 11. Converter of claim 1, wherein said at least one parameter belongs to the group comprising the: response time of the first comparator; time for setting up at least one analog voltage via the digital/analog converter; input signal of the analog/digital converter; operating temperature of the analog/digital converter; method of manufacturing the analog/digital converter.
 12. An integrated component comprising a successive approximation analog/digital converter, which comprises: a successive approximation register supplying a digital/analog converter, and being synchronised by a clock signal coming from a conversion clock; a first comparator comparing an input signal of the analog/digital converter to an output signal of the digital/analog converter and delivering a first comparison signal; and a dynamic adaptation circuit, which dynamically adapts the conversion clock period based on at least one parameter, wherein the dynamic adaptation circuit includes a measurement circuit, which measures at least one of (a) at least one response time of the first comparator or (b) at least one set-up time for at least one analog voltage via the digital/analog converter.
 13. Successive approximation method of converting an analog input signal into a digital output signal, the method comprising: implementing a successive approximation analog/digital converter comprising a successive approximation register supplying a digital/analog converter, a first comparator comparing an input signal of the analog/digital converter to an output signal of the digital/analog converter and delivering a first comparison signal, said successive approximation conversion being synchronised by a clock signal coming from a conversion clock, and dynamically adapting the conversion clock period based on at least one parameter, including measuring at least one of: (a) at least one response time of the first comparison means; or (b) measuring at least one set-up time for at least one analog voltage via the digital/analog converter. 